Effect of changes in intrathoracic pressure on cardiac function at rest and during moderate exercise in health and heart failure

Abstract

This study investigated the effect of changes in inspiratory intrathoracic pressure on stroke volume at rest and during moderate exercise in patients with heart failure and reduced ejection fraction (HFREF) as well as healthy individuals. Stroke volume was obtained by echocardiography during 2 min of spontaneous breathing (S), two progressive levels of inspiratory unloading (UL1 and UL2) using a ventilator, and two progressive levels of inspiratory loading using resistors in 11 patients with HFREF (61 ± 9 years old; ejection fraction 32 ± 4%; NYHA class I-II) and 11 age-matched healthy individuals at rest and during exercise at 60% of maximal aerobic capacity on a semi-recumbent cycle ergometer. At rest, inspiratory unloading progressively decreased stroke volume index (SVI; S, 35.2 ± 5.4 ml m(-2); UL1, 33.3 ± 5.1 ml m(-2); and UL2, 32.2 ± 4.4 ml m(-2)) in healthy individuals, while it increased SVI (S, 31.4 ± 4.6 ml m(-2); UL1, 32.0 ± 5.9 ml m(-2); and UL2, 34.0 ± 7.2 ml m(-2)) in patients with HFREF (P = 0.04). During moderate exercise, inspiratory unloading decreased SVI in a similar manner (S, 43.9 ± 7.1 ml m(-2); UL1, 40.7 ± 4.7 ml m(-2); and UL2, 39.9 ± 3.7 ml m(-1)) in healthy individuals, while it increased SVI (S, 40.8 ± 6.5 ml m(-2); UL1, 42.8 ± 6.9 ml m(-2); and UL2, 44.1 ± 4. ml m(-2)) in patients with HFREF (P = 0.02). Inspiratory loading did not significantly change SVI at rest or during moderate exercise in both groups. It is concluded that inspiratory unloading improved SVI at rest and during moderate exercise in patients with HFREF, possibly due to a reduction in left ventricular afterload.

Figure 1

Heart rate (HR), SV index (SVI) and cardiac index (CI) responses to unloading conditions at rest and during moderate exercise in patients with HFREF (black circles) and healthy individuals (white circles). * main effect for group, ‡ group and condition interaction. S: spontaneous breathing, UL1: first level of unloading, UL2: second level of unloading.

Figure 2

Heart rate (HR), SV index (SVI) and cardiac index (CI) responses to loading conditions at rest and during moderate exercise in patients with HFREF (black circles) and healthy individuals (white circles). * main effect for group, † main effect for loading. S: spontaneous breathing, L1: first level of loading, L2: second level of loading.